1. The Field of the Invention
The present invention relates to hydraulic dampers and, more specifically, hydraulic dampers wherein the pressure within the hydraulic dampers is automatically regulated as the temperature within the dampers varies.
2. The Relevant Technology
Dampers are used in conventional shock absorbers, front forks, and other suspension systems to dampen or absorb an impact or force applied to the suspension system. For example, a conventional damper includes a tubular housing bounding a sealed chamber. The chamber is divided by a floating piston into a primary chamber and a secondary chamber. An incompressible hydraulic fluid is disposed within the primary chamber while a compressible gas is disposed within the secondary chamber. One end of a piston rod having a piston mounted thereon is also disposed within the primary chamber. Orifices extend through the piston so that the piston can slide within the primary chamber of the housing as the hydraulic fluid passes through the orifices.
When a compressive force is applied to the damper, such as when an automobile having shock absorbers hits a bump, the force seeks to drive the piston rod into the primary chamber of the housing. The damper partially absorbs this force by using the force to compress the hydraulic fluid through orifices. When a rebound force is applied to the damper, such as through the application of a spring, the damper again regulates the rebound force by requiring the hydraulic fluid to pass back through the orifices in the piston in order for the piston rod to return to its original position.
Although conventional dampers impart some degree of damping to suspension systems, conventional dampers have significant shortcomings. For example, during extended use, the hydraulic fluid is heated due to the hydraulic fluid being repeatedly forced through the orifices in the piston. As the hydraulic fluid is heated, the hydraulic fluid expands in the primary chamber of the damper so as to move the floating piston and compress the gas within the secondary chamber. In turn, compressing the gas increasing the gas pressure that is applied through the floating piston on the hydraulic fluid and the piston rod. Furthermore, heat from the hydraulic fluid is transferred through the housing and floating piston so as to heat the gas within the secondary chamber. Heating of the gas further increases the gas pressure and thus the force applied against the hydraulic fluid and the piston rod.
As a result of the increased force applied against the piston rod within the primary chamber, a greater external force must be applied to the piston rod to advance the piston rod into the chamber of the damper. Accordingly, for dampers used in an automobile, motorcycle or other forms of vehicle suspension systems, the ride of the vehicle becomes increasingly stiff as the temperature of the hydraulic fluid and gas within the damper increases.
To provide optimal damping in a suspension system, it is generally desirable that the piston rod force and damping properties of a damper be independent and unaffected by change in temperature of the hydraulic fluid and compressible gas contained within the damper. As such, what is needed in the art are dampers that adjust the pressure on the hydraulic fluid within the dampers as the hydraulic fluid expands and contracts with changes in temperature.